305 Small Block Engine Build - The Other Small-Block

Richard Holdener Jul 1, 2010 0 Comment(s)

We liked the fact that in addition to the substantial flow increase, the Trick Flow Super 23 175 heads offered small chambers and valves along with aluminum construction to help eliminate the chance of detonation compared to their cast-iron counter parts. With no loss in compression ratio (something common on head upgrades with a 305), we expected big things from the Trick Flow Super 23 175 heads. We also liked the port volume of the Trick Flow heads, as the 175cc intake ports were not excessive compared to the production heads. It is important to point out that increased port volume does not always result in a loss in low-speed power or even port velocity, as velocity is a function of the flow rate versus the cross section. A larger port that flows a commensurate amount of air will actually produce greater port velocity than a smaller one with less flow (at least at wide open throttle). Larger port volumes can become lazy at part throttle since the flow rate is determined by the throttle opening and not the port itself.

Before upgrading the LG4, we ran it in stock trim to establish a baseline. Our tester consisted of a late-model (meaning hydraulic roller cam) LG4 originally equipped with the factory intake and matching Q-jet 4-barrel carburetor. Since it was missing the factory induction system, we simply installed a suitable cast-iron Q-jet intake and carburetor (from the Carb Shop) along with a set of 13/4-inch long-tube headers. The headers were chosen primarily for dyno fitment, but a set of 15/8-inch headers would work every bit as well and possibly offer slightly more torque. Run with an electric water pump (no accessories), long-tube headers and 37 degrees of total timing, the LG4 produced 224 hp and 308 lb-ft of torque. The mild cam, restrictive heads and factory induction system were equally to blame for the lackluster power numbers, but the 305 still managed to exceed 300 lb-ft of torque from 2,500 rpm (or lower) to 3,600 rpm. Obviously the factory induction system was designed with low-speed grunt in mind.

Knowing that the stock 305 heads and wimpy L03 cam were now holding us back, we pulled both at once and installed the Comp XM270HR cam and Trick Flow Super 23 175 heads. It is possible to upgrade the cam or heads separately, but available dyno time meant we had to be quick. If you have to pick one, we'd opt for the cam first, as the TFS heads might not offer a ton of extra power when saddled with the stock cam (less than 0.400 lift). The cam upgrade will require updating the valve spring package on the stock heads, and if you have to remove the heads for the valve spring upgrade, it is a good time to swap the heads as well.

The Trick Flow Super 23 heads were installed using a set of Fel Pro head gaskets (designed for the small-bore 305) and ARP head bolts. Installation of the heads required no change in pushrod length. We also took the liberty of installing a set of inexpensive 1.5 ratio roller rockers from ProComp in place of the stock stamped steel units. No self-respecting small block should be saddled with stamped steel rockers. The upside of the hydraulic roller cam motor is reduced friction and improved ramp rate to increase power for any given lift and duration combination, but the downside is extra expense (roller cams cost more than their flat-tappet counterparts). To keep costs down, we reused the factory hydraulic roller lifters and timing chain rather than replace them during the cam swap.

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